Thermionic relay circuit



Feb. 16, 1937. L. H. HARRIS 2,070,900

I THERMIONIC RELAY CIRCUIT Filed. June 25, 1932: i *5 She etS Sheet 1 TmLionel Hex-LEFT Harris Feb. 16, 1%? L. H. HARRIS THERMIONIC RELAYCIRCUIT Filed June 25, 1932 s Sheets-Sheet 2 IrTen-lw Lionel Herb EFTHarris MK;

@M,17. L H HAJWS mmwo THERMIONIC RELAY C IRCUIT Filed'JLm 25, 1932 3Sheets-$heet s Lint-1:1 Harbm Harris Patented Feb. 16, .1937

UNITED STATES PATENT OFFICE THERMIONIC RELAY CIRCUIT LionelHerbert'liarrls, London, England, aasignor to Associated ElectricLaboratories, Inc Chicago, 111., a corporation of Delaware ApplicationJune 25, 1932, Serial No. 619,222

. In Great Britain July 2, 1931 10 Claims.

The present invention relates to electrical relay apparatus embodying athermionic valve or a similar electric discharge device for the purposeof producing a change in the direct component of the anode current ofsuch device by the application of a direct or alternating potential toits grid. The chief object of the invention is to provide cheap circuitarrangements whereby a very much greater change in the direct componentof the anode current is obtained than hitherto for a given change inapplied grid po: 'tential, and moreover this change in the directcomponent of the anode current is largely insible to secure satisfactoryoperationof the thermionic relay devices with a high tension source oflower-voltage than would normally be employed; this is particularlyadvantageous in the case of telephone exchanges where the main op-'erating battery normally employed has a voltage in the neighbourhood of50 only. which is comparatively low for the "operation of thermionicvalves.

According to one feature of the invention in a thermionic relay circuitthe anode circuit is ternating current derived from the anode circuit isfed back to the grid thereby increasing the amplitude of the grid swingand changing the direct component of the anode current in consequence ofthe non-linear characteristic of the valve.

The invention will be better understood from the following descriptionof various methods of carrying it into efl'ect which should be taken inconjunction with the accompanying drawings comprising Figs. 1-9. Fig. 1shows its applicabe 500, 600, 750 and 900 cycles per second as is thecase in systems of this kind already in use.

Referring now to Fig. 1, the transmission line is assumed to extend tothe primary of the input transformer ITthe secondary of which is,connected to the thermionic valve V. All the valves shown are of thetype having indirectly heated cathodes the heating filaments beingconnected in series to the exchange battery through a suitableresistance. The valve V acts as an amplifying valve and owing to thefact that the maximum high tension voltage available is that e of theexchange battery, viz. about 50 volts, the output of the valve tends tobe limited to a deflnite level irrespective of the strength of theincoming signals. The output of the valve is passed to the transformer Twhich is a step-down transformer having a large ratio so that thepotential difference across the secondary of this transformer is quitesmall, for instance, less than one volt. As. a further measure tendingto preserve the constant nature of the output a fairly low resistance R,for instance of the order of 5 ohms, may be shunted across the secondaryof the transformer T. As this low resistance only is common .to the fourresonant circuits, interference between them is reduced toa minimum andthis makes for high. selectivity. Each of the four receiving circuits isconnected in the same manner and as regards the first one it comprisesan oscillatory circuit formed of the condenser Cl and the inductance Liin series which is tuned to the particular frequency concerned, say 500cycles. The junction point of the condenser and inductance is connectedby way of the condenser Kl to the grid of the valve VI and the anodecircuit of this valve includes the primary of the transformer Tl inseries with the signal responding relay RI. -The secondary of thetransformer TI is connected across the condenser Kl in series with arectifier XI while the relay RI is shunted by the condenser Fl whichprovides a low impedance path for the alternating component of thecurrent inthe anode circuit. It will be understood that each of. therelays RI. R2, R8 and R4 will 'be provided with suitable contacts, forinstance one front and one back contact by means of which they willcontrol auxiliary relays which in turn act in combination to give thedesired signal.

The operation of the circuit is as follows: When signals are transmittedover the line, they pass to the transformer IT and are extended to thevalve V by means of which they are amplified and fed to the transformerT. The output from the secondary of the transformer T which as alreadyexplained is largely independent of the input voltages and the load onthe transformer is fed to the four tuned circuits in parallel so thatthe circuits corresponding to the received frequencies at any instantproduce relatively high alternating potential at the terminals of thecapacities and inductances. The potentials at theterminals oi theinductances are supplied through the condensers KI, K2, K3 or K4 to thegrids of the valves VI, V2, V3 or V4 by which they are amplified. Theeffect of the transformer such as TI is to transfer power back to thegrid circuit and the effect of the rectifiers is that the condensers KlK2, K3 or K3 are charged in such direction as to produce potential ofconstant sign on the grid so that the current flow in the anode circuitis substantially uni-directional direct current which therefore servesto operate the associated relay.

The change in mean grid potential produced by the condenser charge mayalso have the effect of increasing the. amplification of the valve byenabling it to work on a steeper part of the grid potential-anodecurrent curve than that to which the valve may normally be adjusted bymeans of applied grid biasing voltage. If the potential across the tunedinductance is small due to the frequency to which it is tuned beingabsent from the incoming signal at any instant, with suitable choice ofthe values of the various components it may be arranged that little orno change occurs in the anode current and thus the necessity for amarginal adjustment of the relays is avoided.

It will be understood that the application of the invention tosignalling by means of voice frequency currents of four differentfrequencies is only given by way of example and that it has numerousother applications some of which will now be briefly referred to. Itwill be understood that it is not essential that tuned circuits shouldbe employed and the whole of the alternating current input of mixedfrequencies may be utilized to operate the receiving relay or similardevices in which case as previously pointed out, greater sensitivity isobtained than if the rectifying arrangement were omitted.Modified-operation may be obtainedby reversing the rectifier andadjusting the grid bias so that sufilcient anode current normally fiowsto operate the. relay while on receipt of a signal the effect of therectifier is to increase the negative potential of the grid so that theanode current falls and with suitable adjustment the relay may then bereleased. With larger inputs, however, the effect of the rectifier tendsto be swamped owing to the amplitude of the signals and it may then bearranged that insufllcient change takes place in the anode current torelease the relay.

The two effects just mentioned may each be conveniently combined withresonant or other selective circuits associated with the grid circuit,the anode circuit or the rectifier circuit to give various frequencyselecting arrangements. Moreover both eifects maybe used together inconjunction with a tuned circuit, the arrangement being such that ifcurrents of the correct sigfrequency is arranged to increase thenegativepotential of the grid and thus reduce the anode current. i

This is illustrated in Fig. 2 in which the selectivity is obtained by aresonant circuit consisting of condenser 2| and inductance 22 in therectifier circuit. The arrangement is such that due to currents of thecorrect frequency the condenser 23 is charged by way of the rectifier 24in one direction and serves to decrease the negative potential of thegrid and thus increase the anode current. In response to signals of anyfrequency, however, -the effect of the rectifier 25 is to charge thecondenser 26 in the opposite direction to condenser 23 so as to tend toincrease the negative potential of the grid and thus reduce theanodecurrent. This arrangement is such that the values of the impedances ofthe rectifiers and impedances may be adjusted so that the charge oncondenser 23 is greater than that on condenser 26 when signallingcurrent of the frequencies to which the circuit 2l--22 is tuned, whilewith another frequency the charge on condenser 26 is greater than thaton condenser 23. Thus the impedance of circuit 2 l--22 maybe adjusted tobe less than that of rectiher 25 and condenser 23 to current of thefrequency with which it is desired to operate the relay while theimpedance of circuit 2l-24 will, of course, be much greater withcurrents of other frequencies. Thus when the tuned frequency is receivedthe voltage across 22 will be greater than that across 2 l--22 and withother than the tuned frequency the voltage across 2 |-22 will begreater. Also the values of the impedance of coil 22 and rectifier 25can'be so adjusted that when both the tuned and untuned frequencies arereceived, the voltage across 26 through rectifier 25 direct from thetransformer obtained from across 2 i- 22 will so nearly equal thevoltage across condenser 23 derived from across the'impedan'ce 22 thatthe grid potential will not be sufllciently changed by the differencein'potential to cause operation of the relay in the anode circuit.Hence-with suitable choice of values it may be arranged that a signal ofcorrect frequency and suificient strength to operate the relay ifreceived alone is unable to produce any operation if mixed with a numberof other frequencies. This provides a convenient means for ensuring thata relay which is to be operated by a. signal of a single voice frequencycannot be operated by ordinary speech currents even if they includecurrents of considerable magnitude of that frequency.

0n the other hand, a circuit without tuning may conveniently be employedto respond to speech currents and this provides an arrangement ofgreater sensitivity for voice operated relays than those hitherto used.With ordinary speech the conditions obtained will usually vbe that therelay will operate at each accented syllable and consequently if theresponding relay is arranged to control a relay provided with a copperslug so as to. be slow to release it is easily arranged that this latterrelayzemains operated so long as speech is taking place. Such anarrangement is illustrated in Fig. 3 in which speech currents generatedby the microphone 30 are applied to the grid of the valve 3|. by way ofthe transformer 32 to vary the grid potential. The

aovasco transformer 33 in the anode circuitin response to the variationsin the grid potential serves to feed power back to the grid. circuit byway of the rectifier 36 so as to charge the condenser 35 and reduce thenegative grid potential as previously described for Fig. 1, thusincreasing the sensitivity of the arrangement for operating the relay 36in the anode circuit. This relay at its contact 31 closes a circuit forthe relay 38 provided with a copper slug which due to its slow releasecharacteristics remains energized as long as" conversation continueswithout a. pause. An adjustable resistance tit serves to vary the gridbias.

One possible application of such an arrangement is to obtain voicesupervision on telephone calls, that is to say the operator is signalledowing to the release or the slow relay if no speech takes place over thecircuit for a predetermined period. It will be appreciated that onlysmall alterations are necessary to adapt such arrangement for what maybe termed volume switching, that is to say the control relay will beadjustedto operate when the input to the device supplied from amicrophone reaches a pre-= determined level. The device y also bearranged to test for the presence or tone currents at any point to whichit is-oonnected.

As previously mentioned the application of the invention to telegraphyby Morse or other code permits the use of a lower voltage high tensionsource, or alternatively the use of less components, e. g. fewer valves,or the use of cheaper components, e. g. resonant circuits instead offilters the losses or characteristics incidental to which would.ordinarily preclude their use. An alternative telegraph arrangement maybe em ployed in which grid current, flows over the line and isinterrupted at the transmitting end in order to send the appropriatesignals.

, An arrangement of this type is illustrated in Fig. 4 from which itwill be seen that the general arrangement of the circuit follows thesame prin= ciples as those already described. 'll represents theoperating contact of a Wheatstone tra ter which is shunted by thecondenser 62 and it connected across the signalling lines as and M. s5is the responding relay and t6 the transformer by which feed; back issupplied to the grid circuit by way of a rectifier tl. In this case thevalve may be arranged to oscillate so that alternating current from theoscillation of the valve is superimposed on the grid. The alternatingpotential in the feed-back circuit is applied through the loweradjustable resistance, the rectifier t1, the condenser 62, and over theline to the grid. Due to the rectifying action between thegrid andcathode of the tube a negative potential is accumulated on the grid sideof condenser 62. This potential is sufllclently negative to cause therelay to remain at normal. When contact M is closed condenser 42 isdischarged and the posi-- tive potential across the upper variableresistance is impressed on the grid. This positive potential causessufilcient plate current to flow and operate the relay. Thisarrangementhas been found to work' satisfactorily over very wide rangesof line resistance and also with a comparatively poor line insulation.

The actual circuit details for obtaining what may be called rectifiedreaction are also capable of considerable modification. For instance asshown in Fig. 5 full wave rectification employing four rectiflers inthe'well-known bridge connection' may be employed instead of thehalt-wave rectifier arrangement shown in Figs. 1-4. It will be seen thatthe secondary of the transformer bl in the anode circuit is connected totwo opposite corners of the bridge formed by the rectihers 52-55 and thegrid circuit is connected across the opposite corners together with acondenser 85. During the positive hall cycle the amplified current in heanode of the tube causes the condenser 56 to assume a positive charge onthe grid side by way of 5c and as and during the negative half cycle thecondenser SE is charged in the same sense through rectifiers E52 and as.

A modification is shown in Fig. 6 in which a somewhat similar bridgearrangement is used but the bridge consists of the two rectiflers ti andc2 and two condensers 6t and 6 3. This arrangement it will beappreciated gives voltage doubling but otherwise operates insubstantially the same manner as previomly described. The amplifiedcurrent. in the anode circuit of the tube during the positive cyclecharges the grid side of'the condenser 5 3 positive through rectifier 62and during. the negative cycle charges the condenser 53 in the samesense through rectifier iii to double the voltage.

As a further alternative thebias potential provided by rectification ofthe A. C. component of the anode current may be applied to the gridthrough a. high leak resistance or the order oi 160,000 ohms instead orby way of a condenser directly connected to the grid. Such anarrangement is shown in Fig. 7 where the output from the teed-backtransformer M is applied by way oi. rectifier l2 and high resistance itto the grid of the valve It.

Fig. 8 shows a. further modification in which thetransformer in theanode circuit is dispensed with by making use of a double woundresponding relay the second winding of which supplies the feed-back tothe grid circuit. Thus the anode current passing through the left-handwinding of the responding relay ill induces corresponding currents inthe right-hand winding which are rectified by the rectifier E32 andapplied through the secondary of the input transformer to the grid ofthe valve 53.

A further alternative also dispensing'with a transformer is shown inFig. 9 in which the coupling-is purely electrical instead ofelectromagnetic. In this case the input is passed to the transformer 9|the secondary of which is connected to the grid circuit of the valve 82which has the relay 93 in its anode circuit. A connection from the anodealso extends by way of condenser t l to the junction point of therectiilers 95 and 96 which are connected in the same sense across thefurther condenser v9'l which in turn is connected to the cathode and thesecondary of the input transformer 9| The amplified alternating currentat the plate of tube 82 during a positive halt cycle induces a positivecharge to flow from the right-hand side of the condenser t1 to thebottom side or condenser 94 through rectifier 96. During the negativehalf cycle the posicuit for said valve, means including said gridcircuit responsive to the receipt of signalling current for generatingundulating current in said anode circuit, a plurality of feed-backcircuits each including connections directly coupling the grid circuitto its own anode circuit, the first feed-back circuit having means forreducing the mean negative potential of the grid to increase the anodepotential in response to signals of a particular frequency, the secondfeed-back circuit having means for increasing the mean negativepotential of the grid to reduce the anode potential in response tosignals of different frequencies, and a responding relay connected tosaid anode circuit operative by said increased potential in the anodecircuit only in case said signals are substantially wholly of saidparticular frequency.

2. In a thermionic relay circuit, a thermionic valve, a grid circuit forsaid valve, an anode circuit for said valve, means including said gridcircuit responsive to receipt of signalling current for generatingundulating current in the anode circuit, a plurality of feed-backcircuits directly coupling the grid circuit to its own anode circuit,the first feed-back circuit including a rectifier responsive to changesin current in the anode circuitfor applying a uni-directional potentialto said gridcircuit to reduce the mean negative grid potential of thegrid to in turn increase the anode potential in response to signals of aparticular frequency, the second feed-back circuit including a rectifierresponsive to changes in current in the anode circuit for applyinguni-directional potential to said grid circuit to increase the meannegative potential of the grid to in turn decrease the anode potentialin response to signals of different frequencies, and means operative bythe increased potential in the anode circuit only in case said signalsare substantially wholly of said particular frequency.

3. In a thermionic relay circuit, a thermionic valve, a grid circuit andan anode circuit for said v'alve,a transformer having its primaryincluded in said anode circuit, a tuned circuit including a condenserand a coil resonant to a particular frequency, said tuned circuitshunted across the terminals of the secondary of the transformena firstrectifier connecting the point between the coil and condenser of thetuned circuit to the grid, a first condenser connected in shunt of acircuit including said first rectifier and the coil of the tuned circuitin series, a second rectifier and a second condenser in series connectedin shunt of said secondary, means including said grid circuit responsiveto receipt of signalling current for generating undulating current inthe primary in the anode circuit, said first and second condenserscharged over their shunt connections in response to changes in currentin the primary and secondary of said transformer, the impedances of thetuned circuit and rectifiers being such that on receipt of signalsof'only said particular frequency the charge on said first condenserreduces the mean negative grid potential to increase the anode potentialwhile the receipt of different frequencies irrespectiveof whether one ofsuch frequencies is said particular frequency, charges said secondcondenser to neutralize the charge on the first condenser and to therebyincrease the mean negative grid potential to decrease the anodepotential.

4. In combination, a thermionic valve including a cathode and an anode,a cathode-anode circuit including a source of current, a respondingrelay connected in said circuit between the cathode and the anode andresponsive to the flow of direct current therein, a grid in said valvefor exerting control over the cathode-anode current according to thepotential on the grid, circuit connections for maintaining a potentialon said grid, means effective when said responding relay is to be causedto respond for superimposing an alternating potential on said gridpotential to thereby superimpose an alternating current on thecathode-anode current, a second grid circuit inductively coupled to thecathodeanode circuit to obtain power therefrom when the said alternatingcurrent is superimposed on the cathode-anode current, and a rectifyingdevice so connected in the second grid circuit as to produce analteration of the mean grid potential and cause a consequent alterationof the mean cathode-anode direct current when power is obtained from thecathode-anode circuit, whereby the responding relay is caused to respondto the altered mean cathode-anode direct current.

. 5. In combination, a thermionic valve including a cathode and ananode, a cathode-anode circuit including a source of current, a grid in'said valve for exerting control over the cathode anode current accordingto the potential on the grid, circuit connections for maintaining apotential on said grid, means effective intermittently for superimposingan alternating potential on said gridpotential to thereby superimpose analternating currenton the cathode-anode direct current component, asecond grid circuit inductively coupled to the cathode-anode circuit toobtain power therefrom when the said alternating current is superimposedon the cathodeanode current, a rectifying device so connected 7 in thesaid second grid circuit as to produce an alteration of the mean gridpotential and a consequent increase of the mean cathode-anode currentwhen power is obtained from the cathodeanode circuit, and a respondingrelay associated with the cathode-anode circuit and arranged and adaptedto respond to the increase of the mean cathode-anode direct currentproduced as set nating current on the cathode-anode current,

a. second grid circuit inductively coupled to the cathode-anode circuitto obtain power therefrom when the said alternating current issuperimposed on the cathode-anode current, said second grid circuithaving two branches, means for dividing.

the power obtained from the cathode-anode circuit between the twobranches selectively dependent upon the frequency of the alternatingcurrent superimposed on the cathode-anode current, a rectifying deviceconnected in one branch of the said second grid circuit so as to producean alteration in one direction of the mean grid potential and theconsequent alteration in one direction of the mean cathode-anode currentwhen amplified power is obtained through such branch from thecathode-anode circuit, and a second rectifying device so connected inthe second branch of the second grid circuit as to produce an alterationin the opposite direction of the cathode-anode circuit through the saidsecond branch of the second grid circuit.

7. In combinatioma thermionic valve including a cathode and an anode, acathode-anode circuit including'a source of current, a grid in saidvalve for exerting control over the cathodeanode current according tothe potential on the grid, circuit connections for maintaining apotential on said grid, means for intermittently superimposing analternating potential on said grid potential to thereby superimpose analternating current on the cathode-anode current, a

second grid circuit inductively coupled to the v cathode-anode circuitto obtain power therefrom when the said alternatingcurrent issuperimposed'on the cathode-anode current, said second grid circuithaving two branches, means for dividing the power obtained from thecathodeanode circuit between the two branches selectively dependent uponthe frequency of the in the second branch of the second grid circuit asto produce an alteration in the opposite direction of the mean gridpotential anda consequent alteration in the opposite direction of themean cathode-anode current when power is obtained from the cathode-anodecircuit through the said second branch of the second grid circuit, and aresponding device associated with the cathodeanode circuit and arrangedand adapted so as to respond to an alteration of the mean cathodeanodecurrent only when the alteration is in a given direction from the normalmean value, as

-'controlled through only one of the two said branches of the secondgrid 0kg.

8. In a thermionic valve circ t arrangement wherein the normalcathode-anode current is maintained by virtue of a normal gridpotential,

quenoies on the normal cathode-anode current,

a grid circuit inductively coupled to'the cathodeanode circuit to obtainpower therefrom when analternating current is superimposed on the normalcathode-anode current, said grid circuit being composed of two sections,a rectifying ,de-

vice connected in one section so as to produce an alteration in the meangrid potential. in one direction and a consequent alteration of the meancathode-anode current in one direction responsive to power obtained fromthe cathode anode circuit over such section of the grid circuit, arectifier similarly connected in the' other section but in thereversedirection so as to have an opposing effect upon the mean gridpotential and consequent opposing eflfect upon the mean cathode-anodecurrent responsive to power obtained from the cathode-anode circuitthrough the saidsecond section. and means for causing the power in thefirst section of the said grid circuit to be at a peak responsive tocurrent of substantially a given frequency being superimposed on thecathode-anode current, while the power obtained in the said secondsection of the .grid circuit is substantially independent of thefrequency of the superimposed cathode-anode durrent within wide limits.a

) 9; In combination, a telegraph line incoming to a thermionic valve, asignal-responsive device controlled through the anode-cathode circuit ofthe valve according to the mean value of the anode-cathode current, aself-oscillating circuit for the valve including the telegraph line,means at the distant end of the telegraph line for opening and closingthe self-oscillating circuit to send desired signals over the lineandthereby cause the valve to start oscillating and stop oscillatinaccording to the desired signals, and means including a rectifierdireptly connected to the grid circuit and inductively coupled to theanode-cathode circuit of the valve for causing the mean anode-cathodecurrent to vary according to whether thevalve is oscillating or not,whereby the said signal responding device is enabled to respondaccording to the desired signals.

10. In combination, a thermionic valve having a cathode, an anode, and agrid, a cathode-anode circuit including a source of current and aresponding device operable according to the mean value of thecathode-anode current, means effective when the responding device is torespond for superimposing an alternating current on the cathode-anodecurrent, a pair of rectifiers connected in circuit between the grid ofthe valve and a source of grid potential, and a connection from a pointin the cathode-anode circuit to the junction of said rectifiersincluding a condenser, whereby alternating current passes from thecathode-anode circuit through the condenser to' the rectifiers-andcauses an alteration of the grid potential and a consequent alterationof the mean cathode-anode current so as to bring about a response ofsaid-responding device.

LIONEL HERBERT HARRIS.

